The present invention concerns a method for heating a living body by high frequency current and an apparatus therefor.
The method of heating a living body by using high frequency current utilizes a phenomenon that high frequency current changes to heat when applied to a dielectric substance such as the living body and many reports have been presented in recent years for the therapeutical effect of the method on malignant tumors.
In the conventional high frequency heating method, thermotherapy is carried out by putting a region including portion intended to be heated of a living body between two opposed plate-like electrodes and applying a high-frequency current between the electrodes from a high-frequency power generator.
It has been difficult by the method to heat the portion intended to be heated, up to a temperature needed for therapy if it is situated at a deep inside, because those portions other than the portion intended to be heated may also possibly be heated since the high-frequency current flows substantially in parallel in the region between the opposed electrodes, because a subcutaneous fat layer tends to be heated more intensely than endotract organ tissues due to the difference of electrical constants (electrical conductivity, dielectric constant) between the subcutaneous fat layer and endotract organ tissues, and because there is a risk of patient's complaining of undesirable feeling of heat or of burning patient's epidermal tissues, etc. due to stronger generation of heat in the subcutaneous fat layer than in a portion adjacent to an electrode body.
In view of the above, there has been proposed, in the U.S. Pat. No. 4,676,258, a method of using a first electrode structure having a first electrode surrounded with a flexible and gastight bag-like member made of silicone rubber or the like and having a mechanism for supplying and discharging a coolant to the inside of the bag-like member and a second electrode structure, situating the first electrode structure (heating electrode structure) near the portion intended to be heated, while situating the second electrode structure having a second electrode (non-sensitive electrode structure) with an electrode surface larger by several times or more than the first electrode on the outer circumference of a living body, supplying a high-frequency electric current between the two electrodes, thereby forming an intense electric field distribution near the first electrode structure, selectively heating the portion intended to be heated, and monitoring the temperature at the surface of the living body or controlling the generated high-frequency power based on the information from a temperature sensor situated to the outer surface of the bag-like member.
However, in the above-mentioned method, the indication by the temperature sensor strongly undergoes the effect of the temperature of the coolant for cooling, which may lead to over heating or insufficient heating than required thus giving no insurance for the effective heating of the lesional portion.
Accordingly, it has been strongly demanded at present for the development of a method and an apparatus capable of performing a predetermined heating without the over heating or the insufficient heating and under a quantitative control in heating a living body by way of high frequency current.